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Heat, Work & Metabolism In Chemistry

To begin understanding the interrelationships between and among heat, work and metabolism, as well as its relation to chemistry, it would make sense to define each concept separately. Heat is a form of interaction between two systems, or areas within an object, with different temperatures (law of thermodynamics), and then, in the absence of work, only in the direction of the colder body (second law of thermodynamics). Hence, ultimately, heat pertains to energy transfer in atoms, molecules and other particles that comprise matter. When objects in high temperature interact, the result is high heat transfer.

Chemical reactions (such as burning), nuclear reactions (such as fusion taking place inside the Sun), electromagnetic dissipation (as in electric stoves), or mechanical dissipation (such as friction) all result in high heat transfer (Baeyer, 1998). In the 1830s, the French mathematician Gaspard-Gustave Coriolis invented the term work for the product of force and distance (Max, 1957). Thus, in physics, mechanical work is the amount of energy transferred by a force, or the force applied through a distance when the two share the same direction.

In thermodynamics, thermodynamic work is the quantity of energy transferred from one system to another (Joule, 1845). In the SI system of measurement, work is measured in joules (symbol: J). The rate at which work is performed is power. Metabolism pertains to a set of chemical reactions that take place in living cells as the basis of life. Through metabolism cells are able to maintain their structures and eventually, reproduce. There are two distinct divisions in the process of metabolism: catabolism and anabolism.

In catabolism, the cell breaks down complex molecules to produce energy. In anabolism, the cell uses the produced energy from catabolism to build complex molecules (Smith & Morowitz, 2004). Chemistry is the science of matter at the atomic to molecular scale, dealing primarily with collections of atoms (such as gases, molecules, crystals, and metals). Chemistry deals with the composition and statistical properties of such structures, as well as their transformations and interactions to become materials encountered in everyday life (Stahl, 1730).

From the separate definitions above, it is clear that heat and work are technically studied in the field of physics, particularly in thermodynamics. Metabolism, in contrast, is largely in the territory of chemistry, since in itself it is a series of chemical reactions. However, since heat and work play different roles in the process of metabolism — as heat is the end result of the transfer of energy in the site of metabolism, and work exists as a as a unit of measure of the result of energy transfer — the three of them separately and together are all linked to chemistry.

In the experiment of German physiologist Max Rubner (Spencer, 1985), he demonstrated that the heat of oxidation of a food is the same whether the reaction takes place in the body or in a combustion calorimeter. In the experiment, which effectively studied animal metabolism, Rubner made measurements on animals in calorimeters and used these date in relation to measurements of food taken in for digestion and feces excreted. Subsequently, the same experiment practically showed that as a result of metabolism, the body’s energy is produced by combustion (which is related to heat), and spent through work or heat exchange to the surroundings.

Meanwhile, Spencer’s (1985) experiment showed that the law of conservation of energy applies to metabolism. The law of conservation of energy states that the total amount of energy in the universe is constant, although energy can be transformed from one form to another. This is the first law of thermodynamics in Physics. Hence, in studying metabolism, a law in physics was employed to establish itself in a chemical study, since metabolism in itself is a set of chemical reactions. The human body needs to maintain a body temperature of around 37±1°C.

In order to keep this, heat production must be compensated through heat exchange and by work (Spencer, 1985). The key for this heat exchange lies in the process of the chemical reactions brought bout by digestion of food and simultaneously with that, metabolism. As to how much heat and work could affect metabolism, chemical researches were done to illustrate the points. Hence, heat, work and metabolism are all together subjects of chemical studies, too.

References:

Jammer, M. (1957). Concepts of Force. Dover Publications, Inc..ISBN 0-486-40689-X. Joule, J. P. (1845) “On the Mechanical Equivalent of Heat”, Brit. Assoc. Rep. , trans. Chemical Sect, p. 31, read before the British Association at Cambridge, June Perrot, P. (1998). A to Z of Thermodynamics. Oxford University Press. Smith E. & Morowitz, H. (2004). Universality in intermediary metabolism. Proc Natl Acad Sci U S A 101, 13168-13173. Spencer, J. N. (1985). Heat, work and metabolism. Journal of Chemical Education, 62, 571-574. Stahl, George, E. (1730). Philosophical Principles of Universal Chemistry.

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